High molecular weight polyisobutenes with molecular weights up to several 100,000 Dalton have long been known and the production thereof is described, for example, in H. Güterbock: Polyisobutylen und Mischpolymerisate, pages 77 to 104, Springer, Berlin 1959.
Polyisobutenes with molecular weights of 500 to 5,000 Dalton are produced with the assistance of Lewis acid catalysts, such as aluminum chloride, aluminumalkyl chlorides or boron trifluoride and usually have less than 10 mol % of terminal double bonds (vinylidene groupings) and a molecular weight distribution (dispersity) of between 2 and 5.
A distinction is drawn between these conventional polyisobutenes and “highly reactive” polyisobutenes, which have an elevated content of terminal vinylidene groupings of greater than 60 mol %. Highly reactive polyisobutenes have a considerable market share and are used, for example, as an intermediate for the production of additives for lubricants and fuels, as described, for example, in DE-A 27 02 604. These additives are produced by initially producing polyisobutene/maleic anhydride adducts, in particular polyisobutenyl succinic anhydrides, by the reaction of predominantly terminal double bonds of the polyisobutene with maleic anhydride, which are then reacted with certain amines to yield the finished additive. Since it is mainly the terminal vinylidene groupings which react during adduct formation with maleic anhydride, whereas, depending upon their position, the double bonds located further within the macromolecules do not give rise to any or any distinctly lower conversion without the addition of halogens. The proportion of terminal vinylidene groupings in the molecule is an important quality criterion for this type of polyisobutene.
Further quality criteria for polyisobutenes for the stated intended application are the average molecular weight and the molecular weight distribution, also known as dispersity, of the macromolecules contained in the polyisobutene. In general polyisobutenes with average molecular weights (Mn) of 500 to 5,000 Dalton are used as intermediates for the production of the mentioned lubricant and fuel additives.
When isobutene is polymerized, polyisobutene products are obtained, the polyisobutene components of which, i.e. the polyisobutene macromolecules, have a random molecular weight distribution of a greater or lesser width. The wider the molecular weight distribution of these polyisobutenes, the greater the content thereof of polyisobutene macromolecules having relatively low or relatively high molecular weights, which are less suitable for the mentioned intended application.
It is accordingly advantageous to produce highly reactive isobutenes having moderate molecular weights with the narrowest possible molecular weight distribution, in order to reduce the proportion of unwanted, relatively low or high molecular weight polyisobutenes in the resultant product and thus to improve the quality thereof.
According to the teaching of DE-A 27 02 604, reactive polyisobutenes comprising up to 88 wt.% of terminal double bonds can be obtained by boron trifluoride-catalyzed polymerization of isobutene at temperatures of −50 to +30° C. and residence times of less than 10 minutes. A value of no lower than 1.8 is found for the dispersity of the polyisobutenes produced in this manner.
Polyisobutenes with similarly high proportions of terminal double bonds, but with a narrower molecular weight distribution are obtainable if partially deactivated catalysts are used, such as for example complexes prepared from boron trifluoride, alcohols and/or ethers. Processes of this type are described, for example, in EP-A 145 235, U.S. Pat. No. 5,408,418 and WO 99/64482.
While reaction temperatures of above 0° C. are disclosed in the above cited referenced and the Examples, therein only give rise to an elevated content of terminal double bonds of greater than 80% if temperatures of distinctly below 0° C. are used.
It is apparently possible to produce polyisobutenes with a content of up to 95 mol % of terminal double bonds using the gas phase process of U.S. Pat. No. 3,166,546 and the process of U.S. Pat. No. 3,024,226, in which a boron trifluoride/sulfur dioxide gas mixture is used as the catalyst. These polyisobutenes are characterized on the basis of the results of infrared spectroscopy. However, investigation by 13C nuclear magnetic resonance spectroscopy (13C NMR spectroscopy) of the polyisobutenes produced according to said processes revealed a content of at most 40 mol % of terminal double bonds.
U.S. Pat. No. 4,227,027 discloses boron trifluoride-catalyzed alkyl transfer reactions, wherein the catalysts are adducts of boron trifluoride and diols or polyols at temperatures of 40 to 120° C. When this process was applied to the polymerization of isobutene using a boron trifluoride/1,2-butanediol adduct as catalyst, the only product to be obtained was diisobutylene. Polyisobutene was not formed.
Another process for the production of highly reactive polyisobutenes involves living cationic polymerization of isobutene with subsequent dehydrochlorination, as is described, for example, in U.S. Pat. No. 5,340,881. This process yields up to 100% of terminal double bonds, but requires low temperatures and a complex solvent mixture, which unnecessarily complicates recycling of the unreacted starting materials.
Accordingly, highly reactive polyisobutenes with an average molecular weight of 500 to 5,000 Dalton and a content of terminal vinylidene groupings of greater than 80 mol % are only obtained if temperatures of below 0° C. are used. Such cooling is associated with considerable costs, which reduce the economic viability of the process.
An object of the present invention was to develop an economic process, which operates at temperatures of above 0° C. and yields the described highly reactive polyisobutenes.
It has now been found that such a process may be achieved if monomeric, solvent-stabilized transition metal complexes with weakly coordinating anions are used as the catalysts.